Patent GB-858374-A (GB)
Title: Character recognition equipment
IPC: G06V30/20
Filed: 1958-11-21
Abstract: 858,374. Automatic character reading. STANDARD TELEPHONES & CABLES Ltd. Nov. 21, 1958 [Nov. 27, 1957], No. 37539/58. Addition to 825,597. Class 106 (1). In apparatus for recognizing a character shape, the character is first simulated as a pattern of electric signals in a resistance matrix as described in the parent Specification and connections are made from the intersection points to magnetic core circuits which produce digitized statements as to the existence of certain predetermined shape elements. The shape elements, which are shown in Fig. 1, are as follows : S, the exposed end of a line; W, a continuing line; L, a curved line open to the left; R, a curved line open to the right; O, a curved line open on top; U, a curved line open underneath, and G, a closed curved line. The character is sensed by one or more photocells scanning it in raster pattern, or by a mosaic of photo-cells. At each point of the matrix which covers the character a decision is made as to whether it shall be considered a black, or a white point. At corresponding points on the resistance matrix, Fig. 2, a voltage is applied for a black point (shown as black dots) and no voltage for a white point. Elements S, Wand G.-The outputs of the decision circuits which provide '' black " or " white " signals are applied to the connection points Kn of the matrix through circuits, as shown in Fig. 3. If the shape element S exists at point Kn, the current required to maintain the " black " voltage is large since the point is largely surrounded by points having no voltage. For similar reasons the current required to maintain the voltage where the shape W exists is less. Where the shape G exists the point Kn has no signal of its own but being surrounded by " black " points, tends to assume the black potential. The circuit of Fig. 3 distinguishes between these three conditions. Initially the cores U1 and U2 are set. Where the shape S exists the current J1 is sufficient to reset core U1. Core U2 is not reset because of the opposing action of current J2 in winding W24 flowing from the point Kn to earth. Where shape W is present the current J1 is less but still sufficient to reset core U1. It is insufficient, however, to oppose the action of current J2 and core U2 is reset by this current. In the case of shape G, there is no current J1 but a current J2 is derived from the surrounding " black " points. Core U2 is reset but core U1 remains set. If neither core resets, an indication is given that no character exists at the point Kn. The states of the cores are read out and gated together in appropriate combinations to derive signals indicating the presence of the S, W or G shapes. Elements L, R, O and U.-The existence of a curved line in the upper part of the numeral 2, Fig. 6, is indicated by circuits which study the variations of potential along the horizontal lines such as G. The lines P1-P4 are equipotential lines and samples on line G are shown in Fig. 7a to form a curve increasing at a decreasing rate to the point K7 which, being a point covered by the character image, is at maximum potential. The rate of change of potential is shown in Fig. 7b and the second differential in Fig. 7c. The negative portion of this last curve means that the increase of potential is at a negative rate when moving from left to right, and this is the criterion of a curved line open to the left. To determine whether the second differential is negative, each group of adjacent three points, such as K4, K5 and K6 is connected as shown in Fig. 8, there being a chain of cores, one for each point. The core Ukn has windings W1 and W2 connected in opposition, the former connected between points Kn - 1 and Kn and the latter between points Kn and Kn + 1. Currents flow according to the difference between the potentials at these points. Since the potentials in Fig. 7a increase in the range K4-K6 at a decreasing rate, a greater current will flow in winding W1 than in winding W2. The core is adjusted so that it will switch if this condition exists and will give an output from winding W4 when reset by a read-out pulse on winding W3. This signal indicates a curved line open to the left. A curved line open to the right is detected by a similar circuit with the core biased to switch when the right-hand potential difference is greater. Since points such as K7 which are covered by a character give rise to indeterminate differentials, these points must be excluded from the test for a negative second differential. For this purpose every reset winding is short-circuited by a transistor which is biased to conduct when the core is as associated with a point at " black " potential. Groups of lines GO and GW in the top and bottom halves each have two chains of cores detecting negative second differentials from the left or right. Their outputs are gated together to determine whether the shape elements L and R exist in the upper or lower halves of the character. The determination of the shape elements O and U can be made in the same way as elements L and R except that the scanning lines are vertical instead of horizontal. However, the L and R elements with elements S, W and G are sufficient for identification without elements O and U. Character identification.-The shape elements S, W and G are looked for in the four quadrants (upper and lower, right and left-hand) of the matrix. This information is sufficient to indentify some of the ten digits but the L and R elements are necessary for unambiguous identification of the others. The occurrence of an L-shape in the upper half of the matrix produces a LO signal and in the lower half a LU signal. The four signals LO, LU, RO and RU are almost sufficient to identify the ten digits but confusion would arise between "3" and "8." By using circuits detecting combinations of these signals and the signals S, W and G signals unambiguous identification of the ten digits is obtained. Specification 825,598 is referred to.